U.S. patent number 3,660,181 [Application Number 04/821,095] was granted by the patent office on 1972-05-02 for blasting slurry compositions containing calcium nitrate and method of preparation.
This patent grant is currently assigned to Intermountain Research & Engineering Company, Inc.. Invention is credited to Robert B. Clay, Melvin A. Cook, Lex L. Udy.
United States Patent |
3,660,181 |
Clay , et al. |
May 2, 1972 |
BLASTING SLURRY COMPOSITIONS CONTAINING CALCIUM NITRATE AND METHOD
OF PREPARATION
Abstract
Slurry blasting compositions of low water content and high
density, including substantial proportions of calcium nitrate as an
oxidizer component, can be sensitized in various ways to produce
economical explosive compositions. Sensitizers may include aluminum
powder, granular explosives such as smokeless powder, TNT, etc.; a
particularly preferred sensitizer or fuel is ethylene glycol. Solid
carbonaceous fuels and conventional thickeners may be added. The
calcium nitrate may be produced directly from burned lime with
nitric acid and/or other nitrates.
Inventors: |
Clay; Robert B. (Bountiful,
UT), Cook; Melvin A. (Salt Lake City, UT), Udy; Lex
L. (Salt Lake City, UT) |
Assignee: |
Intermountain Research &
Engineering Company, Inc. (N/A)
|
Family
ID: |
25232488 |
Appl.
No.: |
04/821,095 |
Filed: |
May 1, 1969 |
Current U.S.
Class: |
149/2; 149/21;
149/44; 149/61; 149/76; 149/41; 149/60; 149/75 |
Current CPC
Class: |
C06B
47/14 (20130101) |
Current International
Class: |
C06B
47/00 (20060101); C06B 47/14 (20060101); C06b
001/04 (); C06b 019/00 () |
Field of
Search: |
;149/41,44,60,61,75,76,2,21 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sebastian; Leland A.
Claims
What is claimed is:
1. A pumpable and pourable aqueous slurry blasting composition of
low water content and high sensitivity, comprising a liquid phase
which includes a solution of powerful oxidizer salts selected from
the group which consists of inorganic nitrates, chlorates and
perchlorates and including at least 10% by weight, based on the
total composition, of calcium nitrate, said liquid comprising water
and ethylene glycol and including a viscosity-increasing agent in
the liquid phase per se to impart thereto a viscosity sufficient to
entrap and hold tiny bubbles of gas dispersed in said phase, a
sufficient quantity of gas in the form of tiny bubbles being
dispersed throughout said liquid phase to substantially enhance the
sensitivity of the whole composition to detonation, and a storage
stable, strongly cross-linked thickener or gel former selected from
the group which consists of polysaccharide gums and starches in
proportions sufficient to permanently hold said gas bubbles
dispersed in situ and also to inhibit segregation of solid
particles suspended in the liquid phase and inhibit intrusion of
borehole water into said composition.
2. Composition according to claim 1 which contains at least 8% of
ethylene glycol and wherein the thickener is cross-linked by a
combination oxidation-reduction cross-linking system.
3. Composition according to claim 1 wherein the slurry contains
sufficient gassing agent to hold its density below 1.2 grams per
cubic centimeter under a pressure of 50 psi.
4. Composition according to claim 1 in which there is at least 20%
by weight, based on total composition, of calcium nitrate.
5. Composition according to claim 1 which includes at least 8% of
ethylene glycol.
6. Composition according to claim 1 which includes at least 10% of
calcium nitrate, at least 8% of ethylene glycol, and not more than
8% of water, not including water of crystallization associated with
said calcium nitrate.
7. Composition according to claim 1 which includes at least 5% of
ethylene glycol, at least 10% of calcium nitrate, an
oxidation-reduction cross-linked gel former, and sufficient gassing
agent to keep the slurry density below 1.2 g/cc. under a pressure
of 50 psi.
8. Composition according to claim 7 which includes finely divided
aluminum as a fuel.
9. Composition according to claim 7 which includes at least 8% of
ethylene glycol, at least 20% of calcium nitrate, and which is
sensitive to detonation in a 2-inch column at 10.degree. C by a
standard booster.
Description
BACKGROUND AND PRIOR ART
In recent years, explosive blasting slurries, containing aqueous
solutions of ammonium nitrate and other powerful inorganic
oxidizers plus thickeners, fuels and sensitizers, have come into
extensive use, particularly in the hard rock mining and
construction industries. These slurry compositions are commonly
made up of an aqueous solution of ammonium nitrate, to which sodium
nitrate may be added. The solution is thickened with guar gum
and/or starch to a viscous heavy liquid or gel, and sensitized
usually with high energy fuels such as powdered aluminum and/or
self-explosives such as TNT. In some cases the liquid component has
included non-aqueous but water-compatible liquids, such as
alcohols, glycols, amides such as formamide, and analogous
nitrogen-containing liquids having fuel value as well as having the
solvation or extender properties of liquids. Typical of such
slurries are those described in U.S. Pat. No. 2,930,685 and U.S.
Reissue Pat. No. 25,695 to Cook and Farnam, also in U.S. Pats. Nos.
3,249,474, 3,249,476, and 3,249,477, 3,382,117, and others. Some of
these have suggested possible use of calcium nitrate as an
ingredient of such slurries. As far as the present inventors are
aware, however, no substantial or practical use has been made of
this ingredient.
One reason that calcium nitrate has not been used to any
substantial extent is the fact that it is quite insensitive. As a
matter of fact, aqueous slurries containing most of the usual
inorganic oxidizers are quite difficult to detonate. Considerable
effort has been expended in developing slurries which are
"sensitive" enough for practical use as industrial explosives.
Thus, the use for this purpose of small quantities of very finely
divided heat-producing metal, such as aluminum, or of aluminum
assisted by other ingredients, is well known. Also, the use of
self-explosive particles distributed throughout the slurry, such as
granules of TNT, grains of smokeless powder, and the like, and
combinations of such with aluminum, etc., are known. Furthermore,
the sensitivity-contributing effect of tiny gas bubbles, especially
of entrapped air bubbles, has been recognized and suggested as
being desirable, as mentioned in some of the patents referred to
above. Even with these effective sensitizers, however, calcium
nitrate as a substantial and significant ingredient of blasting
slurry compositions has not been used in practice and its use, as a
rule, has not been considered feasible, as far as the present
inventors are aware.
The presence of water in such slurries, of course, detracts greatly
from their sensitivity. However, in order to maintain the desired
liquidity or fluidity for mixing, pumping and/or pouring the
slurries into boreholes for immediate use, or into packages for
storage, substantial proportions of some kind of liquid usually are
required. Thus, commercially usable slurries ordinarily contain as
much as 12 to 20% by weight, or more, of water. Somewhat lower
proportions can be used if fluidity for pumping is not needed.
Where the particulate materials are present in a variety of
particle sizes, aluminum particles for instance, less liquid is
required for a given viscosity. See U.S. Reissue Pat. No. 25,695.
Generally speaking, any combination of calcium nitrate as an
oxidizer, with its known insensitivity, and of relatively high
water content in a blasting slurry would be expected to be so dead
or insensitive as to be impractical. Moreover, calcium nitrate
usually contains considerable water of crystallization and this
would appear to be a deterrent to its use. The content of such
water of crystallization in calcium nitrate varies somewhat from
place to place, depending on storage conditions and on the various
processes of manufacture. It usually runs about 14%, more or less,
by weight in commercial calcium nitrate.
Contrary to the disadvantages suggested above, the present
inventors have found that calcium nitrate can be used effectively
and in substantial proportions in aqueous blasting slurries, with
several advantages that the prior art seems not to have recognized.
Among such advantages are the following:
a. Calcium nitrate slurries can be made having relatively high
density or specific gravity, as compared with slurries made up
primarily of ammonium nitrate and other conventional
ingredients.
b. The slurries of the present invention require considerably less
water to render them fluid, due to release of the water of
crystallization normally present in calcium nitrate, when made by
the process of this invention; the water requirements can be
reduced further and advantageously by substitution of ethylene
glycol or analogous organic liquid for part or most of the
water.
c. The cost of calcium nitrate slurries is relatively low.
d. Calcium nitrate per se can easily be produced in situ and in the
field and, using cheap starting materials.
e. Where explosive sensitizers are used, proportions required can
be substantially reduced, as compared with general practices in the
art.
f. The congelation temperature or "fudge" point of slurries
containing calcium nitrate can be lower, other things being equal
or, alternatively, larger total salt proportions can be used
without raising the fudge point.
Other advantages will appear as this invention is more fully
described hereinafter.
A further advantage of the use of calcium nitrate, according to the
present invention, is the possibility of using products of higher
density. Conventional slurries often are sensitized in part by
inclusion of fine bubbles of air or other gases provided their
densities are not too high. They do not appear to respond very well
to sensitization by such gas bubbles when made with densities
exceeding about 1.4 grams per cubic centimeter. This limitation
appears not to apply in the same degree to the slurries of the
present invention.
A significant aspect of the present invention, which was mentioned
briefly above, pertains to the "fudge" point or congelation
temperature of the composition. In present commercial practice, a
solution of the oxidizer salt, which is usually ammonium nitrate or
a combination of sodium nitrate and ammonium nitrate, is dissolved
in hot water. Thereafter, fuels and/or sensitizers, etc., in solid
particulate form and usually insoluble in the liquid are added to
the solution. As the resulting slurry cools, it reaches a point at
which the salts in solution begin to precipitate, causing a rapid
thickening or solidification. The temperature at which this occurs
is the so-called "fudge" point and it varies with the composition.
Obviously, it is desirable to have a fudge point low enough that
necessary mixing and pumping of the slurry can be accomplished
before the material starts to solidify, that is, before the fudge
point is reached.
The use of calcium nitrate, contributing liquid as it does by
release of at least some of its water of crystallization either
lowers the fudge point or, alternatively, makes it possible to use
more total oxidizer in the solution without raising the same fudge
point. This is an important aspect of this invention.
DESCRIPTION OF PREFERRED EMBODIMENT
The invention will be explained further by giving specific examples
of compositions incorporating it.
A series of samples of explosive slurry were made up, simply using
calcium nitrate to replace part of the normal ammonium nitrate
and/or sodium nitrate, as follows. Parts shown are percentage by
weight.
---------------------------------------------------------------------------
TABLE I
A B C D Ammonium nitrate 42 45 45 55.2* Sodium nitrate 9 10 10 --
Calcium nitrate 37 36.5 36.5 36.8* Water 12 8.5 8.5 8.0* Guar gum
thickener 0.1 0.1 0.1 0.25 Ethylene glycol 0.2 -- -- 0.5 Propylene
glycol -- 1.0 1.0 -- TNT ("Pelletol") 16 -- -- -- Gilsonite 3.7 6.0
6.0 -- Aluminum--coarse -- 9.0 9.0 -- Aluminum--fine -- 1.0 1.0 --
Smokeless powder -- -- -- 28 Density -- 1.40 at 1.34 at --
54.degree. C. 54.degree. C.
__________________________________________________________________________
composition A was prepared by dissolving the sodium nitrate first
in warm water, 70.degree. C, then adding the ammonium nitrate and
calcium nitrate together. In these tests a Norwegian calcium
nitrate was used. This composition was not tested for detonation
but would be expected to be detonable and it had a good
consistency. In Compositions B and C test charges were made up in 2
inches, 2 1/2 inches, and 3 inches diameters, in lengths six times
the diameter. The 2 inches charges failed to detonate completely
but the larger charges were all fired successfully with a standard
booster. For Composition D the proportions starred made up 100% of
the solution. For sensitizer, 28 parts of HSSP double base
smokeless powder was used. This product had a solution density
(before addition of smokeless powder) of 1.61. Density after
addition of the SP was not determined. This product fired in a
2-inch column with a standard "2A" booster.
Another series of tests were made, starting with a standard
oxidizer solution S.sub.1 which was made up of the following
ingredients, parts by weight.
Ammonium nitrate (AN) 32.5 or 35.9% Calcium nitrate (CN) 37.0 or
40.8% Sodium nitrate (SN) 5.5 or 6.06% Water 5.5 or 6.06% Ethylene
glycol 10.0 or 11.03% Guar gum--commercial 0.2 or 0.22%
The sodium nitrate was dissolved first in the water and then the
calcium nitrate and ammonium nitrate were added together to the
solution. Temperature of this mixture was about 70.degree. C. Water
of crystallization released from the calcium nitrate helped
maintain liquidity. This total mixture had a pH of about 4.5 and an
oxygen balance of about +11%.
The guar gum was dispersed in the ethylene glycol and the resulting
dispersion added to the oxidizer mixture. The resulting composition
was a solution having somewhat higher viscosity than an ordinary
aqueous solution of the same salts. It was cooled down to about
50.degree. C before adding particulate fuel or sensitizer
ingredients in the form of various pre-mixes mentioned below. This
solution had a "fudge" point (congelation temperature) of about
35.degree. C.
In order to cross-link the gum to get higher viscosity and thus
prevent segregation of suspended fuel particles, etc., a
cross-linking agent or in some cases a combination of
oxidizer-reducer agents was used. A typical agent, designated "A,"
was a 50/50 solution of potassium or sodium dichromate. Gallic acid
or potassium antimony tartrate was used as reducing agent in a
number of examples. In some of these, gassing agents such as
nitrous acid or ammonium, sodium or potassium nitrite were added in
very small proportions, sometimes with melamine or thiourea to
accelerate aeration. Hydrogen peroxide was used in some cases,
along with traces of potassium iodide or manganese dioxide to
catalyze decomposition. In some cases it was difficult to thicken
slurries with pH above 3.0. In these a small amount of nitric acid
was used to lower the pH slightly. Thus 0.55 cc of 58% nitric acid
per 100 g. of slurry brought pH down to 3.0 and 0.2 cc brought it
to a level between 1.0 and 2.0. Thiourea speeded up the thickening
and also increased the gassing rate when ammonium, potassium, or
sodium nitrite were used. Gassing agents are useful not only to
reduce density but also to increase sensitivity. Numerous gassing
agents are available, as will readily be understood by those
skilled in the art.
Slurries were made up using ground pitch or gilsonite alone, or
finely divided aluminum alone as dry fuel. The gassing rate of such
slurries, using KNO.sub.2, did not change significantly with either
fuel but initial thickening was somewhat better with aluminum.
Gassing and reasons therefor are discussed further below. A
self-cross-linking guar gum was a satisfactory thickener, as long
as pH was not too high. So was potato starch. As little as 1%
potato starch gave good initial thickening but for the increased
gel stability needed for prolonged storage, 3% was used. With
lesser quantities of potato starch, the gelled slurries seemed to
break down after standing a few days. While potato starch is used
in these examples, any of the strongly cross-linked
polysaccharides, i.e. gums and starches, may be used.
Several examples were made up starting with the above solution
S.sub.1, using about 0.16 cc of concentrated (58% or 70%) nitric
acid per 100 grams to reduce pH and 0.2% of KNO.sub.2 as a gassing
agent. Potato starch (PS) was used as thickener. In some cases
extra ethylene glycol (EG) was added.
---------------------------------------------------------------------------
TABLE II
Added Ex. % Solution Thickener Fuels Modifiers
__________________________________________________________________________
E 94 3% PS 3% ground 0.05% thiourea pitch 0.06% KNO.sub.2 0.3 cc.
"A" F 87.2 3% PS 3% ground 0.2% thiourea pitch 0.12% KNO.sub.2 6%
EG 0.3 cc "A" G 80.2 3% PS 10% fine 0.05% thiourea atomized 0.12%
KNO.sub.2 aluminum 0.3 cc "A" 6% EG
__________________________________________________________________________
composition E had a density of 1.14 g/cc. and was fired
successfully in 3-inch, 2 1/2-inch and 2-inch diameter columns at
0.degree. C, using a standard booster. A similar composition having
higher density 1.22, failed in a 2-inch column at the same
temperature. Example F, with a density of 1.19 fired successfully
under similar conditions as did Example G with a density of 1.06.
Critical density for a 2 1/2-inch column appears to be about 1.20.
Hence, where a column of slurry explosive is tall, and where its
own hydrostatic head, plus stemming, compresses it supplemental
aeration or gassing may be needed. The sensitivity at 0.degree. C
is considered quite remarkable for a slurry explosive containing no
self-explosive and no paint grade aluminum powder.
The compositions of Examples E, F and G were treated with 0.2, 0.1
and 0.3 cc, respectively (per 100 grams) of concentrated (58%)
nitric acid to reduce the pH to where thickening could be
accomplished successfully with potato starch. Additional
experiments were made to obtain a thickening system that would be
effective without reducing the pH by use of acid.
Using solution S.sub.1, as above, and cross-linking the thickener
by an oxidation-reduction combination of agents, i.e. 0.2 to 0.3%
agent "A" (K.sub.2 Cr.sub.2 O.sub.7 in water) and gallic acid (GA)
in proportions of 0.02 to 0.5, good thickening was realized in
slurries of high pH (4.3 to 5.0). In some of these aluminum was
used as a fuel, to supplement the ethylene glycol in the solution.
In others a guar meal was the fuel and in still others a
combination of aluminum and guar meal (GM) was used. Significant
data are given in Table III. Each of these contained 3% by weight
of potato starch as a thickener. Penetration of the slurry as an
indication of its viscosity was measured by use of a specially
designed cone-shaped penetrometer. These readings were taken after
5 minutes and after 10 minutes, shown in this order; likewise,
densities are given after 5 minutes, 30 minutes and 24 hrs. to show
effectiveness of gassing.
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TABLE III
Ex. % S.sub.1 Fuel % X-link pH % KNO.sub.2 Pen. Density Agents
g./cc.
__________________________________________________________________________
H 87.5 8.5 Al 0.05 GA 4.6 0.4 250 1.14 180 1.02 0.78 J 86.9 8.5 Al
0.05 GA -- 1.0 170 0.89 -- 0.75 0.43 K 89.8 9.6 GM 0.05 GA 4.8 0.4
240 0.82 180 0.73 0.57 L 88.4 5.0 Al 0.05 GA 5.0 0.4 250 0.87 6.0
GM 180 0.75 0.60 M 87.9 8.5 Al 0.05 GA 4.8 0.4 230 0.90 3.0 GM 180
0.77 0.60 N 86.15 10 Al 0.5 GA -- 0.6 -- 0.82 300 -- 0.69
__________________________________________________________________________
blasting slurries must be at least reasonably stable in
composition, consistency and density, particularly when they are
packaged or are to be used in boreholes where they may stand 24
hours or more before use. If the gel breaks down (or viscosity
decreases) so as to permit segregation of the suspended fuel and
sensitizer particles (called "pre-mix") the composition may become
worthless. If it loses its aeration or entrapped gas it may become
so insensitive that it will not detonate. Likewise, if placed in
deep boreholes, the lower part of the explosive column may be under
sufficient hydrostatic or superimposed pressure that the charge
will not detonate, or at least will not detonate all the way. A
particular object, realized in this invention, was to obtain stable
gassed slurries that can be detonated in 2 1/2-inch columns or
larger, at temperatures as low as 5.degree. C and under pressures
of up to 50 psi. The products described in Table III above meet
these requirements. Many, perhaps most, of the blasting slurries of
the prior art fall far short of the latter requirement.
The use of ethylene glycol with its fuel value and its
low-temperature solvent properties, as a significant ingredient is
one important feature. Another is the use of calcium nitrate which
makes it possible to use higher total proportions of oxidizer for a
given fudge point. A mixture of oxidizers containing ammonium
nitrate and sodium nitrate also is usually preferred. As noted
above, a fudge point as low as 35.degree. C is quite remarkable and
some of these products have such. The use of an effective
cross-linking system such as dichromate-gallic acid or other
oxidation-reduction combinations, which are reasonably independent
of pH is important. While acid can be added to slurries to reduce
their pH and improve the thickening or gelling effect of starches
and gums, this is often quite undesirable. Slurries of low pH
*(high acidity) are excessively corrosive to mixing and pumping
equipment. Hence, a thickening system not dependent on low pH is
advantageous. In situ mixing and pumping of blasting agents has
many advantages. Separate ingredients which are non-explosive
individually can be combined at the mine and pumped directly to the
borehole before they get too viscous for pumping through hoses.
Thus controlled viscosity, which builds up slowly enough to permit
mixing and pumping but rapidly enough to prevent segregation of
solids or borehole water intrusion in the gel, is important.
Compositions of this invention have all these desirable properties,
including density control when the slurry is under the pressure of
a tall column in a borehole. They may include various combinations
of inorganic oxidizer salts such as nitrates, chlorates and
perchlorates.
Preferably, the slurries of this invention include at least 5% by
weight of ethylene glycol as a fuel and liquid extender, at least
10% of calcium nitrate, a stable thickening system, and enough
gassing agent to keep the slurry at density not exceeding 1.20 g/cc
under 50 psi pressure. Particularly preferred are slurries
containing at least 8% of ethylene glycol, at least 20% of calcium
nitrate, and less than 8% added water. propylene glycol can be used
in lieu of part or all of the ethylene glycol; see Table I
above
Variations in ingredients and proportions, including use of
self-explosive particles in some cases and other types and
varieties of fuels and other ingredients can be made within the
scope of this invention as will be obvious to those skilled in the
art.
* * * * *